<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    .main {
      display: flex;
      flex-direction: column;
      height: 100vh;
    }

    header,
    footer {
      height: 40px;
      background-color: aqua;
    }

    div {
      flex: 1;
      background-color: burlywood;
    }
  </style>
</head>

<body>
  <div class="main">
    <header></header>
    <div></div>
    <footer></footer>
  </div>
</body>

</html>